Mario grew up in Baltimore and other working-class neighborhoods in Baltimore County, Maryland.[3] He lived with his grandmother, who raised him while his single mother struggled with a drug addiction.[3] Mario said at the age of four that he wanted to become a singer. His mother supported his dream and bought him a karaoke machine. Mario joined a musical group in Milford Mill Academy with the oldest son of comedienne Mo'Nique and best friend Jaye Brebnor and also his younger god sister Chea Tyler. Barrett learned to play the piano and used that skill as the basis for his melodies and songs. He was discovered at age eleven and signed by producer Troy Patterson, after singing "I'll Make Love to You" at a Coppin State College talent show.[3] Mario attended Milford Mill Academy up until the tenth grade where he was inspired by his music teacher, during his early teen years, and was offered a record deal at the age of fourteen, signing with Clive Davis' J Records.[3] His musical influences include Stevie Wonder, Marvin Gaye, Sam Cooke, Nat King Cole, Brian McKnight, Boyz II Men, Usher, and Joe. His first introduction to the music industry was the Dr. Dolittle 2 movie soundtrack in 2001. He sang a captivating performance of the Stevie Wonder classic "You and I" at Clive's Grammy party in 2002, and began recording an album.

Mario began recording his debut album entitled Mario in July 2001, nearly a year before releasing it in March 2002. The album's lead single "Just a Friend 2002", which was a cover of Biz Markie's hit, was an instant success, peaking at #1 on the charts. Follow up singles were "Braid My Hair" and "C'mon" . He was the opening act on the Scream Tour 3, which featured B2K, Marques Houston, Nick Cannon, Jhené Aiko, and AJA. As of 2006, his debut album has sold over 700,000 copies.[3] During this period, he became a draw in the teen market.[3]

In February 2006, Mario filed a lawsuit against his former manager, Troy Patterson, alleging that Patterson had paid him $50,000 for the sale of more than 3 million records, which was later found to be false accusations. Mario was later sued by Patterson and lost. Mario's new manager is J. Erving and he was chosen by Mario.[4]

In an interview with DJ "Z", Mario stated that problems with the record label caused the album launch to be pushed back 6–8 months.[7] In 2008, Mario competed on season six of Dancing With the Stars. He was partnered with Karina Smirnoff. They were eliminated in week eight of the competition.

In a 2009 interview with Rap-Up.com, Mario said that "Soul Truth Entertainment" was his new entertainment company.[8] Before the release of his third album Go, Mario confirmed in an interview with that he was working on a new album "by the time school starts back up, like after next summer” “But there's really even more than that, 'cause I'm gonna start recording, like, [at] the end of January".[9] The album is involving a wide range of producers and songwriters such as Darkchild, Babyface, Polow da Don, RedOne, and CJ of Charlio Productions, Malay, Jazze Pha, Stargate, KP, Tricky Stewart and The-Dream as confirmed by Mario.[10][11][12] Mario said that he would like to work with no more than 4 producers for this album.[9] Mario has described this album as World music, an old school R&B influenced with a modern dance pop sound.[12] The album is being described as his “most personal, colossal album of his career.”

In January 2009, Mario became the face of Pelle Pelle's European Spring/Summer campaign with various press shots running through the first part of the year.[13] For his fourth album D.N.A., the lead single "Break Up" was released on April 28, 2009. The song features Sean "The Pen" Garrett and Gucci Mane.[14] In the US, the song, have peaked at number 2 on the Hot R&B/Hip-Hop Chart and 15 on the Billboard Hot 100, becoming Mario's most successful single in five years. The single has been recently certified Gold by the Recording Industry Association of America (RIAA) for a shipment of over 500,000 units as a .[15] "Thinkin' About You", was released as the second single reaching number forty-five on the Hot R&B/Hip-Hop Chart. "Stranded" never labelled as the third single due to the limited airplay that it received. Lack of interest led to the single being cancelled, although in January 2010 the song entered on the Billboard Hot R&B/Hip-Hop Songs peaking at number 84. "Ooh Baby" was later confirmed to be the third single from the album, it peaked on the week of March 19, 2010 debuting on the Billboard Hot 100 at number 95. The entire album was made available for the public to listen to on his Myspace page before its release. The album debuted at number nine on the Billboard 200, selling 38,000 copies in its first week, becoming Mario's lowest-selling debut in the United States. So far, it has sold 93,385 copies in the US.

Mario is currently working on his fifth studio album, which is titled Evolve. Prior to this, Mario recorded a whole album with Producer Rico Love from 2010 to mid-2011 under the tentative title Restoration. Songs from this album included My Bed, Killa, Bermuda, The Walls, Recovery, Falling Down and Computer Love. Furthermore, during Mario's appearance on BET's 106 & Park on July 10, 2013, Mario stated that he felt the album recorded with Rico Love did not feel part of his career plan and he scrapped that album and went on to record his current album which was set to be released in September 2013, but was delayed to 2014. For his fifth album, Mario has stated the album will include "Love songs, Ballads, Club Records and General R&B", and has said there will be no EDM Records on this album. Mario Took Writers Jeremiah "Sickpen" Bethea and Jimi Bonet under his wing amongst others to write for this album. Production on the album include the likes of Glass John, BAM ALEXANDER, Pollow da Don and possibly Ne-Yo.

In an interview with Vibe magazine, Mario was asked what direction he was trying to go with on his fifth album; his answer was, "I wanna give as much honesty as I can. I want to be honest, but grab the attention of everybody, but still compete so when you hear it on the radio it’s pushing the envelope. The melodies coming out of me now are unorthodox— melodies I've never expressed before". He also confirmed he has five tracks that are definitely going on. "These tracks are like movies, they are intense", he added. Nevertheless, the album will probably feature a song centered on his mother, written by himself.[16] In August 2011, RCA Music Group announced it was disbanding J Records along with Arista Records and Jive Records. With the shutdown, Mario (and all other artists previously signed to these three labels) will release his future albums on the RCA Records label.[17][18]

Through his official Twitter page, on May 17, 2013, Mario confirmed that he has been working with Polow Da Don, for the lead single "Somebody Else" featuring rapper Nicki Minaj was already recorded and released.[19][20] The song was made available in the iTunes Store on May 21, 2013. He also thanked to Polow Da Don, Jeremiah Renaldo, Nicki Minaj and CJ Hilton for composing the song. He stated that his album, will be released in September 2013 and may include guest appearances from Nicki Minaj, J. Cole & Sevyn Streeter. "Fatal Distraction" will be his next single.[21] Mario announced during a USTREAM interview with Music Choice, his album will be released in October 2013 but was pushed back.[22][23] The second single "Fatal Distraction" was released on September 10, 2013.[24] The album will be released in early 2014.[25]

Mario's Do Right Foundation was established on March 2008 to educate and inspire kids who suffer from the drug addictions of their parents.[30] In May, Mario published a notice on the Facebook page of the foundation, saying that he had been in a studio in Miami all night re-recording the hit song "Do Right" from his 2007 album "Go". This remix "Do Right" will be the theme song for Mario's Do Right Foundation. The song debut is expected to be at this year's African American Heritage Festival in Baltimore.[31]

MTV aired a special on October 21, 2007, "I Won't Love You to Death: The Story of Mario and His Mom," which dealt with his mother's heroin addiction. The documentary is about how the singer strives for help to stop his mother's addiction. While doing this, he seeks help from family and friends.[32] Mario wrote a letter to his mother stating how appreciative he is and begs her to stop her addiction. At the end of the letter he says, "I love you, but I won't love you to death".[33] The documentary, produced by Gigantic! Productions, won a 2008 Prism Award for its accurate portrayal of drug abuse.[34] Mario has also written a song titled Do Right that is dedicated to his mother. This song explains his mother's addiction and how it affected his childhood.[35] The song is featured on his third album Go.

In 2009, Mario endorsed PETA in the campaign against killing animals entitled "Ink, Not Mink". He tells: "Be comfortable in your own skin, and let animals keep theirs".[36] Mario has homes in Baltimore, Atlanta and Los Angeles.[3]